This is a national study supported by NIH to determine if Type I diabetes can be prevented in individuals who are positive for Islet cell antibodies but have not developed glucose intolerance. It has recently become possible using islet cell autoantibodies (ICA) to identify individuals who have a 50 percent chance of developing IDDM within the next 5 years. Primary relatives of patients with IDDM have a tenfold increased risk of having ICA and this is the group that will be targeted in this trial. Patients who are classified as intermediate risk or high risk for developing IDDM will be offered one of two randomized intervention protocols. Those patients in the high risk category (>50% of developing IDDM within 5 years) will be offered a randomized trial of no treatment versus daily subcutaneous injections of long-acting insulin to attempt to prevent the development of diabetes. There are three separate stages of this study, each of which have separate objectives: STEP 1: SCREENING: Initial eligibility screening of relatives for IDDM risk by determining ICA. (500 screened locally) STEP II: STAGING: Definition of risk categorized by staging of ICA positive patients as to the risk of developing clinical IDDM. (2 subjects) STEP III: INTERVENTION: Implementation of the insulin intervention protocol for patients in the high risk category. (1 subject - discontinued injections but will have a glucose tolerance test. Patients that are in step 2 or step 3 will be studied in the General Clinical Research Center at University Hospitals. Screening and staging are done by Dr. Douglas Rogers at the Cleveland Clinic Foundation. To date approximately 500 individuals have been screened but only 1 subject has qualified for the parenteral insulin treatment study (done at this GCRC).